Grass Seed Calculator
Enter your lawn area, pick your grass type, and choose whether you are starting a new lawn or overseeding an existing one. The calculator applies university-standard seeding rates to give you the exact pounds (or kilograms) of seed you need, a cost estimate, and a breakdown of the math.
How to calculate how much grass seed you need
The formula is straightforward: multiply your lawn area in square feet by the seeding rate for your grass type (in pounds per 1,000 sq ft), then divide by 1,000. For example, a 2,000 sq ft lawn planted with Tall Fescue from bare soil needs 2,000 x 10 / 1,000 = 20 lb of seed. Overseeding the same area needs only half that: 10 lb. The key variable is the seeding rate, which varies significantly across grass species. Cool-season grasses like Tall Fescue and Perennial Ryegrass need 8-10 lb per 1,000 sq ft for new lawns, while warm-season species like Bermuda and Zoysia need only 1-3 lb because they have larger, heavier seeds and spread aggressively by runners once established.
New seeding vs. overseeding: why the rate changes
A new lawn on bare soil has no competition, so seed can be spread densely and most germinating seedlings will survive. Overseeding an existing lawn means seedlings must compete with established grass for water, light, and nutrients, so the recommended rate is usually half the new-lawn rate - the existing turf fills the remaining gaps. Overseeding is common in late summer for cool-season lawns to thicken thin areas or repair damage without the cost of a full re-establishment. If you scalp the lawn and dethatch before overseeding, you can use the higher new-lawn rate for better results.
Cool-season vs. warm-season grass types
Cool-season grasses (Kentucky Bluegrass, Tall Fescue, Perennial Ryegrass, Fine Fescue) grow most vigorously in spring and fall when temperatures are 60-75 degrees F. They are common in the northern United States, Canada, and northern Europe. Seed cool-season species in late August through October for best results. Warm-season grasses (Bermuda, Zoysia, Bahia, Centipede, St. Augustine, Buffalo) thrive in summer heat and go dormant in winter. They dominate lawns in the southern United States, Australia, and tropical regions. Seed warm-season species in late spring when soil temperatures are consistently above 65 degrees F. Choosing the wrong type for your climate is the most common reason for seeding failure.
How to prepare your lawn for seeding
Proper seedbed preparation is more important than the seed itself. For new lawns: till the top 4-6 inches, remove rocks and debris, grade for drainage (slope gently away from the house), apply a starter fertilizer (high in phosphorus), and rake to a fine, firm surface. For overseeding: mow the existing lawn short (1-2 inches), dethatch if needed, aerate with a core aerator to reduce compaction, and apply seed directly into the aeration holes and over the surface. In both cases, lightly rake seed in or use a slit-seeder for better soil contact. Water lightly twice a day until germination (typically 7-21 days depending on species), then transition to deeper, less frequent irrigation.
Grass type seeding rates
| Grass Type | Season | New Lawn (lb/1,000 sq ft) | Overseed (lb/1,000 sq ft) |
|---|---|---|---|
| Tall Fescue | Cool | 10 | 5 |
| Kentucky Bluegrass | Cool | 3 | 1.5 |
| Perennial Ryegrass | Cool | 10 | 5 |
| Fine Fescue | Cool | 5 | 2.5 |
| Creeping Red Fescue | Cool | 5 | 2.5 |
| Sun and Shade Mix | Cool | 6 | 3 |
| Bermuda | Warm | 2 | 1 |
| Zoysia | Warm | 2 | 1 |
| Bahia | Warm | 10 | 5 |
| Centipede | Warm | 0.5 | 0.3 |
| Buffalo | Warm | 3 | 1.5 |
| St. Augustine | Warm | 4 | 2 |
Standard rates in pounds per 1,000 sq ft from university extension services. Overseeding rates are approximately half the new-lawn rate.
Frequently asked questions
How do I measure my lawn area?
For a rectangular lawn, measure the length and width in feet and multiply them. For irregular shapes, divide the lawn into rectangles, triangles, or circles, calculate each section separately, and add them up. You can also use Google Maps satellite view with the measurement tool, or walk the perimeter with a measuring wheel. Subtract any non-grass areas like garden beds, driveways, and the house footprint.
What happens if I use too much grass seed?
Over-seeding creates overcrowded seedlings that compete intensely with each other for water and nutrients. This results in thin, weak grass rather than thick turf. Dense seedling populations are also more vulnerable to damping-off diseases. More seed is not better - stick to the recommended rate for your grass type and project.
How much grass seed do I need per acre?
One acre equals 43,560 sq ft. Multiply the per-1,000-sq-ft rate by 43.56. For example, Tall Fescue at 10 lb/1,000 sq ft requires 435 lb per acre for a new lawn. Kentucky Bluegrass at 3 lb/1,000 sq ft needs about 130 lb per acre.
When is the best time to plant grass seed?
For cool-season grasses (Fescue, Bluegrass, Ryegrass), late summer to early fall is ideal - soil is still warm enough for germination but air temperatures are dropping, reducing heat stress on seedlings. Early spring is the second-best window. For warm-season grasses (Bermuda, Zoysia, Centipede), late spring through early summer is optimal, once soil temperatures consistently exceed 65-70 degrees F.
How long does it take grass seed to germinate?
Germination time depends on the species and soil temperature. Perennial Ryegrass germinates fastest (5-10 days at 50-65 degrees F). Tall Fescue takes 7-14 days, Kentucky Bluegrass 14-30 days, Bermuda 10-30 days, and Zoysia 14-21 days. Soil temperature, moisture, and seed-to-soil contact all affect germination speed. Using a slit-seeder or raking seed into the soil speeds things up compared to surface broadcast.
Should I use a seed mix or a single grass type?
Mixes (such as Sun and Shade Mix or turf-type tall fescue blends) spread risk across multiple cultivars, so if one cultivar is susceptible to a disease or drought, others compensate. Single-species lawns (like a pure Kentucky Bluegrass lawn) look more uniform but are more vulnerable to a single pest or disease. In most home lawns, a good-quality blend or mix is the practical choice.
What is the difference between lb per 1,000 sq ft and kg per 1,000 m²?
These are the two standard units for seeding rates. The metric equivalent is nearly identical numerically: 1 lb/1,000 sq ft is approximately 4.88 g/m², or 4.88 kg/1,000 m². To convert, multiply lb/1,000 sq ft by 4.88 to get kg/1,000 m², or divide by 4.88 to go the other way.